Placebos work because people who take it believe that they're actually medicine, right? I mean, that's the basic tenet of every modern medical studies, which use placebos as controls.

But can placebos work without any deception? Here's an intriguing study from Harvard Medical School that discovered the surprising healing power of sugar pills:

"Not only did we make it absolutely clear that these pills had no active ingredient and were made from inert substances, but we actually had 'placebo' printed on the bottle," says Kaptchuk. "We told the patients that they didn't have to even believe in the placebo effect. Just take the pills."

For a three-week period, the patients were monitored. By the end of the trial, nearly twice as many patients treated with the placebo reported adequate symptom relief as compared to the control group (59 percent vs. 35 percent). Also, on other outcome measures, patients taking the placebo doubled their rates of improvement to a degree roughly equivalent to the effects of the most powerful IBS medications.

"I didn't think it would work," says senior author Anthony Lembo, HMS associate professor of medicine at BIDMC and an expert on IBS. "I felt awkward asking patients to literally take a placebo. But to my surprise, it seemed to work for many of them."

Seeing as the control group didn't take any pills, the control isn't really as rigorous as it could be as it does not control for the ritual of taking a pill which could contribute to the placebo effect independently of belief in the treatment due to previous experience that associates taking a pill with feeling better. Seeing as this is merely a replication of much older studies with similar findings it would have been more informative and scientifically rigorous to have a group unknowingly taking placebos as an additional control so that not only would the ritual of taking a pill be controlled for, but we can see whether the placebo effect is weakened by knowledge that the pills are placebos.